1. Field of the Invention
The present invention relates to an air-metal secondary battery unit and an air-metal secondary battery module including the same, and more particularly, to an air-metal secondary battery unit that enables discharge and charge, and an air-metal secondary battery module including at least one air-metal secondary battery unit.
2. Description of the Related Art
An electrochemical power source is an apparatus in which electrical energy can be generated through electrochemical reaction. The apparatus includes an air-metal battery such as an air-zinc battery, an air-aluminum battery, and so on. The air-metal battery employs a negative electrode formed of a metal converted into a metal oxide during discharge, and a positive electrode as an air positive electrode film, which is a transmissive film including water molecules, and in contact with oxygen in the air to generate hydroxyl ions.
Such an air-metal battery has various advantages in comparison with a conventional hydrogen fuel cell. In particular, since a fuel such as zinc is plentifully provided as a metal or an oxide thereof, supply of energy provided from the air-metal battery is not visually exhausted. In addition, while the conventional hydrogen fuel cells require recharge, the air-metal battery can be electrically recharged and can transmit a higher output voltage (1 to 4.5 volts) than the conventional fuel cells.
Such an air-metal battery that enables discharge and charge is referred to as an air-metal secondary battery, and the air-metal secondary battery has the air positive electrode film that functions as a positive electrode during discharge and reacts with the air or oxygen supplied from another supply source through the following chemical formula.O2+2H2O+4e−4OH−  [Chemical Formula 1]
A hydroxyl ion generated through the chemical formula moves to a zinc gel, which is a negative electrode gel of the air-metal secondary battery, to form zinc hydroxide on a surface of the zinc gel. Then, the zinc hydroxide is decomposed into zinc oxide and water is discharged to become an alkaline aqueous solution. Such a reaction can be expressed through the following chemical formula.Zn+2OH−Zn(OH)2+2e−Zn+2OH−ZnO+H2O+2e−  [Chemical Formula 2]
The air-metal secondary battery is discharged through the above-mentioned reaction to supply electrical energy to the outside. Then, when the air-metal secondary battery arrives at a discharge limit to stop supply of the electrical energy to the outside, the battery can be electrically charged to be reused.
However, discharge and charge processes of the air-metal secondary battery are repeated as described above, moisture in the negative electrode gel may be reduced and the negative electrode gel, i.e., a mixture of electrolyte and zinc metal, may be cured to make it impossible to reuse the air-metal secondary battery.
In addition, when an electron (2e−) having a negative charge is supplied into zinc oxide (ZnO) upon charge of the air-metal secondary battery, a zinc ion (Zn2+) is reduced into zinc and an oxygen ion (O2−) is separated from the zinc ion. The oxygen ion separated from the zinc ion passes through a negative electrode collector of the air-metal secondary battery to be reduced into oxygen (O2).
As described above, a case of the air-metal secondary battery configured to accommodate the negative electrode gel, the air positive electrode film, and the negative electrode collector may be damaged due to oxygen generated in the air-metal secondary battery upon charge thereof.
Meanwhile, in recent times, as eco-friendly energy has come into the spotlight, research on modularization in which one or more air-metal secondary batteries are connected to constitute a battery module to be used for a vehicle battery that requires a large capacity of electrical energy has been continuously conducted. However, if these problems cannot be solved, commercialization may be impossible.